A frequent consequence of heart attacks is the development of cardiac arrest associated with a heart arrhythmia, such as ventricular fibrillation. Electrotherapy can be performed by delivering an electrical pulse to a patient's heart in order to treat ventricular fibrillation. More particularly, ventricular fibrillation may be treated by applying an electric shock to the patient's heart through the use of a defibrillator. The chances of surviving a heart attack decrease with time after the attack. Quick response to a heart attack by administration of a defibrillating shock as soon as possible after the onset of ventricular fibrillation is therefore often critically important.
In order to be effective, a defibrillation shock must be delivered to a patient within minutes of the onset of ventricular fibrillation. Studies have shown that defibrillation shocks delivered within one minute after ventricular fibrillation may approach up to 100% survival rate. The survival rate falls to approximately 30% if six minutes have elapsed before the shock is administered. Beyond twelve minutes, the survival rate approaches zero.
One way of decreasing the time required to deliver a defibrillation shock to a patient is to greatly increase the availability of defibrillators in proximity with potential patients. Recently, the development of lightweight, relatively low-cost defibrillators has enhanced availability and contributed to decreasing the response time for patients needing treatment. More particularly, low-cost lightweight defibrillators manufactured by Heartstream, Inc. of Seattle, Wash., utilize an impedance-compensating biphasic waveform which has reduced size and cost, thereby increasing the availability of such devices to persons in outside-of-hospital settings. For example, such defibrillators have been deployed on first-response vehicles and to locations where large groups of individuals are gathered, such as in office buildings, corporate campuses, airplanes, health clubs, stadiums, and theaters. Such deployment to many environments contributes to greatly shortening the time from a patient's collapse to the delivery of a first shock.
With greatly increased deployment of such portable external defibrillators, the response time to shock a patient is being greatly reduced. However, an expanded first-response force needs to be trained so as to include a broad range of physician-authorized personnel, such as fire service and ambulance personnel, police officers, flight attendants, security guards, safety officers, and any other health care professional or appropriately trained individual with a duty to respond. Presently, such attempts are being undertaken.
One problem associated with expanding the use of defibrillators to physician-authorized personnel has been the varying degrees of training and skill that such personnel possess. Depending upon the environment in which an external defibrillator is employed, it might be desirable to control the functionality of such defibrillator so that it is tailored to match the level of skill and training that an intended operator possesses. Only through a dramatic improvement in defibrillator access, accompanied by appropriate training and delivered functionality, will sudden cardiac arrest lose its distinction as one of the nation's leading killers.
Prior art electrotherapy devices are known for producing electric shock to treat patients for a variety of heart arrhythmias. For example, manual external defibrillators provide relatively high-level shocks to a patient, usually through electrodes attached to the patient's torso, to convert ventricular fibrillation to a normal sinus rhythm. Similarly, external cardioverters, which are also manual defibrillators, can be used to provide shocks to convert atrial fibrillation to a more normal heart rhythm. Manual defibrillators require a significant amount of training, whereas automatic defibrillators tend to be expensive and invasive. One type of defibrillator is an implantable defibrillator which is relatively expensive, invasive, and requires a reduced level of shock delivery because of a direct current path to a patient's heart. Another type of defibrillator is an automatic external defibrillator (AED) which automatically analyzes patient heart rhythms and delivers electrotherapeutic pulses to a patient's heart indirectly, through the patient's skin and rib cage. Hence, external defibrillators tend to operate at higher energies, voltages, and/or currents.
Hardware and/or software electrocardiogram (ECG) analysis devices and analysis implementations are known within prior art defibrillators, both implantable and external, for detecting heart function so as to characterize a patient's heart condition. Furthermore, such prior art defibrillators are known for generating defibrillator waveforms that are characterized according to the shape, polarity, duration, and number of pulse phases. Typically, such heart function detection and defibrillator waveform generation are carried out via an ECG arrhythmia analysis algorithm and a discharge controller having discharge circuitry, respectively.
One approach for detecting patient heart function is shown in U.S. Pat. No. 5,014,697 to Pless, et al. (incorporated herein by reference). The Pless, et al, patent discloses a two-channel defibrillator having a programmable stimulator. The stimulator provides an assessment of lethal ventricular tachyarrhythmias in determining defibrillation thresholds during implantable defibrillator procedures. An initial test defibrillation shock is delivered to a patient, after which an automatic charging circuit and dual-channel, high-voltage capacitor circuits operate to reduce the time in which a rescue shock can be delivered to a patient. A microprocessor-controlled display system includes an operator interface that provides information parameters regarding the defibrillation shocks being delivered.
Another approach for detecting patient heart function is shown in U.S. Pat. No. 5,620,471 to Duncan (incorporated herein by reference). The Duncan patent discloses an apparatus for applying atrial and ventricular therapies to a patient's heart using an implanted cardiac stimulating device. Atrial and ventricular heart rates are monitored with the device to determine whether the patient is suffering from atrial or ventricular arrhythmia, and to then determine what type of therapy is appropriate for application to the patient's heart. Atrial and ventricular heart rates are compared via an algorithm to determine if the ventricular heart rate exceeds the atrial heart rate and to determine whether the ventricular heart rate is stable. According to one implementation, an early atrial stimulation pulse can also be applied to determine whether the ventricular heart rate follows the atrial heart rate. Therapy is applied to the patient's heart based upon determinations between atrial and ventricular heart rates.
Yet another approach to monitoring and defibrillating a patient's heart is provided by U.S. Pat. No. 5,474,574 to Payne, et al. (incorporated herein by reference). The Payne, et al., patent discloses a cardiac monitoring and defibrillation system configurable as a bedside or an ambulatory unit. Amplification and processing circuitry receives and conditions inputs from sensing apparatus such as electrocardiograms, blood oxygenation sensors, blood pressure monitors, and a cardiac acoustical transducer. Noise and artifact discrimination is implemented to prevent erroneous detection of the onset of cardiac arrhythmias. In response to condition inputs from the monitoring apparatus, a microprocessor controls therapeutic electrical stimulation being delivered to a patient according to a cardioverter/defibrillator step therapy method. A control panel or external programming and monitoring unit can be utilized to program and control the microprocessor. According to one construction, the system includes a bidirectional communication link which allows monitoring and programming of the microprocessor by a physician at a remote location. Additionally, the system provides a method for detecting cardiac arrhythmias and distinguishing between the different types of arrhythmias which may be detected.
One approach for generating and delivering a relatively low-energy multiphasic waveform to a patient is shown in U.S. Pat. No. 5,601,612 to Gliner, et al. (incorporated herein by reference). The Gliner, et al., patent discloses an external defibrillator that automatically compensates for patient-to-patient impedance differences in the delivery of electrotherapeutic pulses for defibrillation and cardioversion. An energy source is discharged through electrodes to the patient to provide a biphasic voltage or current pulse. The delivered biphasic pulse can be altered to compensate for patient impedance differences by changing the nature of the delivered electrotherapeutic pulse, resulting in a smaller, more efficient and less expensive defibrillator.
Other electrotherapy apparatus and methods are shown in Cole, et al., U.S. Pat. No. 5,662,690; Morgan, et al., U.S. Pat. No. 5,549,115; Morgan, et al., U.S. Pat. No. 5,593,426; Morgan, U.S. Pat. No. 5,591,213; and Cole, et al., U.S. Pat. No. 5,611,815, all of which are incorporated herein by reference.
Prior art defibrillators have addressed the problem of detecting a heart condition requiring electrotherapy, and delivering a corresponding therapeutic shock pulse to a patient. However, the deployment of portable external defibrillators to a variety of new settings or deployment environments has placed such devices in the hands of less skilled operators. For example, the placement of such devices on airplanes has provided great benefits in reducing the time before delivery of a first shock. However, the operators of such devices are generally less skilled than operators in the past, even for cases where they are given some degree of training. Accordingly, the placement of such defibrillators into a greater variety of environments subjects the devices to use by a greater variety of personnel having different degrees of skill and training.
Furthermore, providing defibrillators to a wider range of patients, including children and infants, is a natural extension to a goal of providing wider and more rapid access to defibrillators.
Therefore, in an effort to optimize the performance of such devices within a specific environment, it becomes necessary for a manufacturer to tailor operation and functionality of a specific device for an intended user or operator and/or patient. Where the skill level and training of an intended user is well known, an electrocardiogram (ECG) signal analyzer can be designed for an automated defibrillator having a specific combination of functional trade-offs that optimize performance for that intended user. Additionally, there exists a further need to configure a defibrillator for use with different patients.
For example, the placement of such a defibrillator into the hands of a highly-skilled and highly-trained paramedic or physician enables a manufacturer to optimize sensitivity of the ECG signal analyzer, and to impart specificity within the analyzer which enables the operator to make final judgments on whether a patient needs to be shocked. Accordingly, such highly-skilled and highly-trained operators can be provided with additional information about a patient's heart function and condition which enables such highly-skilled and highly-trained operators to make judgment calls based upon whether a patient should be shocked.
On the other hand, if an intended operator is minimally trained and has a minimal skill level, a manufacturer must design a separate ECG signal analyzer for use within the automated defibrillator. A modified arrhythmia analysis algorithm may be employed. Furthermore, hardware changes might also be required in order to deliver a defibrillator that is best suited for use by a low skill and/or minimally trained operator. For example, where a minimally trained operator such as a flight attendant is the likely operator of a defibrillator, it may be appropriate to emphasize specificity over sensitivity, not enabling a significant degree of operator judgment to be exercised in deciding whether a patient is to be shocked. If the AED is used on small children, it may be required to employ an Algorithm Analysis (AA) match to the pediatric electrocardiogram (ECG).
Current prior art defibrillators contain ECG signal analyzers having an arrhythmia analysis implementation (hardware and/or software) which incorporates a fixed set of assumptions and trade-offs, giving no capacity to adapt functionality of the defibrillator to the skill level of the intended operator. Therefore, a manufacturer must design specific and distinct defibrillator devices that are tailored for each specific use for an intended operator having a pre-defined skill level or training. Hence, it becomes necessary for a manufacturer or distributor of such products to maintain a number of different models of defibrillators which are specifically designed to deliver functionality that matches the training and skill level of the intended operator encountered in the deployment environment.
Accordingly, it is likely that a defibrillator designed for use with a low-skilled and little-trained operator will find its way into the hands of an operator in a deployment environment who is highly skilled and highly trained. Such a device will be designed to prevent an operator from making personal judgment calls on whether to deliver a shock to a patient. Hence, a highly-skilled operator will be prevented from making judgment calls on whether or not a patient should be shocked. Such judgment calls become particularly important when dealing with borderline heart rhythms which might be suitable for shocking. Similarly, a defibrillator having an ECG arrhythmia analysis implementation suited for a highly-skilled and highly-trained operator might find its way into the hands of a low-skilled and little-trained operator. A similar, but more complicated, problem occurs here wherein a low-skilled operator is enabled with the power to use operator judgment and potentially apply a shock treatment to a patient having a borderline rhythm group which should not be shocked. A problem may occur if an adult AED is applied to a child, and vice versa.
Hence, a significant problem occurs in that the placement of such environment-specific defibrillator devices might be mis-matched with the operator and/or patient. For the case where a device is sold to an organization, it is likely that they might change the environment in which such device is being utilized. For example, a device that is configured for use with a highly-trained and highly-skilled operator might later be deployed in an environment where a low-skilled and little-trained operator has the device for use. Such occurrence is extremely likely to happen in the event that an organization has already paid for the device, and is faced with having to expend further monies to purchase a device that is reconfigured for an operator having a different skill level.
Therefore, there is a need to provide for a single, common defibrillation device having an ECG arrhythmia analysis apparatus capable of being configured/reconfigured so as to enable deployment/re-deployment for operators having varying degrees of training and skill level or varying patient characteristics. Therefore, it would be desirable to obtain improvements in automated defibrillators that enable the manufacture and assembly of a single, common defibrillator having ECG arrhythmia analysis features capable of being selectively tailored. It would further be desirable to provide a method for reconfiguring such an automated defibrillator to impart a desired degree of functionality to an operator.